Optical axis adjusting method, optical module producing method, optical axis adjusting apparatus, and optical module

ABSTRACT

An optical axis adjusting method for adjusting a tilt angle of an optical axis in two regions optically coupled in a holding member includes the steps of: roughly adjusting the optical axis by irradiating a first region on the holding member with a laser beam; and finely adjusting the optical axis by irradiating a second region on the holding member with a laser beam. One of the two regions is set as a reference point. The first region is located closer to the reference point, while the second region is located further from the reference point.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an optical axis adjusting method, anoptical module producing method, an optical axis adjusting apparatus,and an optical module.

2. Description of the Related Art

In a conventional optical output device in which a light-emittingelement and optical fiber are optically coupled to each other through alens, deviation of an optical axis is corrected to eliminateirregularity in the optical coupling. The supporting component of theoptical fiber is irradiated with a laser beam, and the correction isperformed based on deformation of the spots irradiated with the laserbeam. Such a structure is disclosed in Japanese Laid-Open PatentApplication Publication No. 63-163416, for example. FIG. 1 illustratesthe disclosed structure.

As shown in FIG. 1, an optical output device 100 includes a supportingmember 110 that supports a light-emitting element 140, a supportingmember 120 that supports a condenser lens 150, and a supporting member130 that supports the incident face of optical fiber 160. In thisstructure, the supporting member 130 is spot-fused with a laser beam101. By doing so, the supporting member 130 is deformed so that light141 condensed by the condenser lens 150 is incident upon the incidentface of the optical fiber 160.

So as to obtain a necessary amount of distortion to adjust optical axesin the above conventional structure, however, it is necessary to adjustthe intensity of the laser beam 101 or to increase the number of timesto emit the laser beam 101. As a result, adjusting the intensity of thelaser beam 101 involves sensitive work, and the laser beam 101 isemitted an increased number of times. These problems cause furtherproblems such as a complicated production method and an increase in thecosts.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide an opticalaxis adjusting method and apparatus in which the above disadvantages areeliminated.

A more specific object of the present invention is to provide an opticalaxis adjusting method and apparatus that can perform optical axisadjustment with high efficiency and high precision. Another specificobject of the present invention is to provide a method of easily andefficiently producing an optical module having an optical axis adjustedwith high precision. Further specific object of the present invention isto provide an optical module having an optical axis adjusted with highprecision.

The above objects of the present invention are achieved by an opticalaxis adjusting method for adjusting a tilt angle of an optical axis intwo regions that are optically coupled in a holding member, comprisingthe steps of: roughly adjusting the optical axis by irradiating a firstregion on the holding member with a laser beam; and finely adjusting theoptical axis by irradiating a second region on the holding member with alaser beam, one of the two regions being a reference point, the firstregion being located closer to the reference point, and the secondregion being located further from the reference point.

The above-objects of the present invention are achieved by an opticalaxis adjusting method for adjusting a tilt angle of an optical axis intwo regions that are optically coupled through a lens optical systemheld by a holding member, comprising the steps of: irradiating a firstregion on the holding member with a laser beam, the first region beinglocated on the same side of the lens optical system as a reference pointthat is one of the two regions; and irradiating a second region on theholding member with a laser beam, the second region being located on theopposite side of the lens optical system from the reference point, oneof the first region and the second region being a region in which thetilt angle of the optical axis is roughly adjusted, and the other one ofthe first region and the second region being a region in which the tiltangle of the optical axis is finely adjusted.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects, features and advantages of the present invention willbecome more apparent from the following detailed description when readin conjunction with the accompanying drawings, in which:

FIG. 1 illustrates the structure of a conventional optical output devicein which a light-emitting element and optical fiber are opticallycoupled to each other through a lens;

FIG. 2 is an inner perspective view of the entire structure of anoptical output device in accordance with a first embodiment of thepresent invention;

FIGS. 3A through 3C illustrate deviations of optical axes caused whenthe first housing is welded to the second housing in the structure ofthe first embodiment;

FIGS. 4A and 4B illustrate deviations of optical axes caused between thecondenser lens and the ferrule in the structure of the first embodiment;

FIG. 5 is a graph showing the relationship between the distance from thereference point along the optical axis, and the distance by which acoupled component is moved in a direction perpendicular to the opticalaxis through one-time laser irradiation;

FIG. 6A is a graph showing the optical coupling tolerance of thecondenser lens in the structure of the first embodiment;

FIG. 6B is a graph showing the optical coupling tolerance of theincident face of the ferrule in the structure of the first embodiment;

FIG. 7 is an external view illustrating a rough adjustment region and afine adjustment region on the surface of the trunk part of thesub-housing in the structure of the first embodiment;

FIG. 8A is an inner perspective view of the sub-housing in the structureof the first embodiment;

FIG. 8B is a graph showing the relationship between the amount ofadjustment made with a laser beam of a constant intensity in the roughadjustment region and the amount of adjustment made with the laser beamin the fine adjustment region with respect to the distance from thereference point along the optical axis;

FIG. 9 is an inner perspective view of the structure in which laserwelding has been performed on the first housing and the second housingthat tilt with respect to each other;

FIG. 10A is an inner perspective view illustrating a situation in whichthe rough adjustment region is irradiated with a laser beam emitted froma laser irradiation unit in a first step of an optical axis adjustingmethod in accordance with the first embodiment of the present invention;

FIG. 10B is an external view of the sub-housing having the roughadjustment region irradiated with the laser beam;

FIG. 11A is an inner perspective view illustrating a situation in whichthe fine adjustment region is irradiated with a laser beam emitted froma laser irradiation unit in a second step of the optical axis adjustingmethod in accordance with the first embodiment;

FIG. 11B is an external view of the sub-housing having the fineadjustment region irradiated with the laser beam;

FIG. 12 is a block diagram illustrating the structure of an optical axisadjusting apparatus in accordance with the first embodiment of thepresent invention;

FIGS. 13A through 13C illustrate the operation of an optical axisadjusting apparatus in accordance with a second embodiment of thepresent invention;

FIG. 14A is an inner perspective view illustrating the structure of asub-housing in accordance with a fifth embodiment of the presentinvention; and

FIG. 14B is a graph showing the relationship between the distance fromthe incident face and the amount of adjustment to be made with a laserbeam of a constant intensity in the sub-housing.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following is a description of preferred embodiments of the presentinvention, with reference to the accompanying drawings.

First Embodiment

Referring first to FIG. 2, a first embodiment of the present inventionwill be described in detail. FIG. 2 is an inner perspective view of theentire structure of an optical output device 1 in accordance with thisembodiment. The optical output device 1 is an optical module that can beused as a light source in the field of optical communication and otherfields of technology. As shown in FIG. 2, the optical output device 1includes a main housing 2 and a sub-housing 50. Optical fiber 42 isconnected to the top end of the sub-housing 50 through a connector unit43.

The main housing 2 accommodates a light-emitting element 10, a drivecircuit 11, and a collimate lens 20. The light-emitting element 10 ismade of a semiconductor material such as silicon (Si), gallium arsenic(GaAs), or indium phosphorus (InP). The drive circuit 11 drives thelight-emitting element 10. The collimate lens 20 converts a laser beam 3outputted from the light-emitting element 10 into a parallel beam. Thelight-emitting element 10 and the drive circuit 11 are securely mountedto the main housing 2. The collimate lens 20 is secured by a supportingmember 21. The laser beam 3 outputted from the light-emitting element 10and then converted into a parallel beam by the collimate lens 20 isincident on the exterior of the main housing 2 (the interior of thesub-housing 50) through a window 60 formed in a wall of the main housing2. The window 60 is made of quartz or glass.

The sub-housing 50 is provided outside the window 60, and the laser beam3 emitted from the main housing 2 enters the hollow inside thesub-housing 50. The sub-housing 50 is welded to the main housing 2 by apredetermined laser beam emitting unit, or is bonded to the main housing2 with a solder or some other adhesive. The sub-housing 50 accommodatesa condenser lens 30 that condenses the laser beam 3, and a ferrule 40that is a transmission medium protruding from the optical fiber 42. Thesub-housing 50 is an assembly that includes a first housing 51 thatholds the condenser lens 30 and the ferrule 40, and a second housing 52that holds the first housing 51 with respect to the main housing 2. Thefirst housing 51 holds the condenser lens 30 and the ferrule 40 in sucha manner that the laser beam 3 condensed by the condenser lens 30 isincident onto the incident face 41 of the ferrule 40. The first housing51 has a narrow part 53 that is formed to hold the condenser lens 30.The outer diameter of the cross section (perpendicular to the lightpropagating direction) of the narrow part 53 is smaller than the outerdiameter of the cross section (parallel to the cross section of thenarrow part 53) of any other part of the sub-housing 50. The thicknessof the outer wall of the narrow part 53 may be equal to the thickness ofthe outer wall of any other part of the sub-housing 50, but it is morepreferable to form the narrow part 53 to have a thinner outer wall thanthe outer wall of any other part of the sub-housing 50. The firsthousing 51 and the second housing 52 are welded to the main housing 2 bya predetermined laser irradiation unit, or are bonded to the mainhousing 2 with a solder or some other adhesive. Each of the firsthousing 51 and the second housing 52 may be a single member, or may bean assembly that includes welded or bonded members.

The collimate lens 20, the condenser lens 30, and the incident face 41of the ferrule 40 function as optical coupling components. In thisembodiment, spot irradiation with laser beams (laser beams 6A and 6Bshown in FIGS. 10A and 11A) is performed on the surface of the trunk ofthe sub-housing 50 with a predetermined laser irradiation unit, so as toadjust the relationship (a tilt angle, for example) between optical axesin regions optically coupled through the respective optical couplingcomponents. The spots on the sub-housing 50 irradiated with the laserbeams (6A and 6B) are melted and are then solidified by cooling. Throughthis process, the sub-housing 50 is deformed, and the optical axes ofthe optical coupling components shift. Using the shifting, the positionsand inclinations of the optical axes in regions optically coupledthrough the optical coupling components are adjusted to correctdeviations of the optical axes in different regions to achieve a desiredpositional relationship and desired inclinations. The laser irradiationunit may or may not be the same one as the laser irradiation unit usedfor bonding the housing components. Also, the laser irradiation unit maybe a laser welding device such as a YAG laser device.

In the following, examples of deviations of optical axes caused indifferent regions coupled in the optical output device 1, especiallyinside the sub-housing 50, will be described in detail.

FIGS. 3A through 3C show deviations of optical axes caused when thefirst housing 51 is welded to the second housing 52. FIG. 3A illustratesthe process of welding the first housing 51 to the second housing 52,using the laser irradiation unit (a laser welding device). As shown inFIG. 3A, the second housing 52 is attached to the main housing 2 inadvance. While being positioned to the second housing 52 secured to themain housing 2, the first housing 51 is brought into contact with thesecond housing 52, and is then welded to the second housing 52 by spotirradiation with a laser beam 5A. Here, welded points 5 a are formed inthe spots where the spot irradiation with the laser beam 5A has beenperformed.

If the first housing 51 is welded to the second housing 52 in asituation where the optical axis C4 of the ferrule 40 held by the firsthousing 51 tilts with respect to the optical axis of the light outputtedfrom the main housing 2 (the light being the laser beam 3 outputted fromthe collimate lens 20 in this embodiment), which is the optical axis C2of the collimate lens 20, a gap (θ) is caused between the optical axesC2 and C4 due to the tilting, as shown in FIG. 3B. Such a gap is alsocaused by the difference in the amount of deformation among the weldedpoints 5 a. If the first housing 51 is welded to the second housing 52in a situation where the optical axis C4 of the ferrule 40 held by thefirst housing 51 tilts with respect to the optical axis C2 of thecollimate lens 20 in the X direction and the Y direction on a planeperpendicular to the optical axis C2, a parallel gap (x, y) is causedbetween the optical axes C2 and C4, as shown in FIG. 3C. Such a parallelgap (x, y) may also be caused from differences in the amount ofdeformation among the welded points 5 a.

FIGS. 4A and 4B illustrate deviations of optical axes between thecondenser lens 30 and the ferrule 40. As shown in FIGS. 4A and 4B, ifthe condenser lens 30 and the ferrule 40 are not properly positioned topredetermined positions in the first housing 51, for example, in a casewhere the optical axis C3 of the condenser lens 30 tilts with respect tothe optical axis C4 (see FIG. 4A) or where the optical axis C3 of thecondenser lens 30 and the optical axis C4 of the ferrule 40 deviate inthe X direction and the Y direction (see FIG. 4B), a gap (x, y, θ) iscaused between the optical axis C3 and the optical axis C4, as shown inFIGS. 4A and 4B.

The gap (x, y, θ) causes a decrease in the light quantity of the laserbeam 3 entering the ferrule 40. To counter this problem in thisembodiment, the surface of the trunk of the sub-housing 50 is irradiatedwith a laser beam, so that the optical axes are adjusted by virtue ofthe deformation of the sub-housing 50 caused by the laser irradiation.By doing so, the relationship between the incident face 41 of theferrule 40 and the focal point of the laser beam 3, which involves thepositions and tilts of the optical axis C4 of the ferrule 40 and theoptical axis C3 of the condenser lens 30, and the relationship betweenthe optical axis C2 of the collimate lens 20 and the positions and tiltsof the optical axes C3 and C4, are controlled to increase the lightquantity of the laser beam 3 entering the ferrule 40. Here, the amountof adjustment to be made to the optical axes with a laser beam of aconstant intensity varies with the distance from a reference point setin an optically coupled region that is located on the opposite side ofthe condenser lens 30 from the region between the incident face 41 andthe condenser lens 30. Assuming that the angle 9 of an optical axis tobe adjusted by a laser beam of a constant intensity is constant,regardless of the shape of the sub-housing 50, the distance L by whichthe optical axis is moved through one-time laser irradiation becomeslonger (L₁>L₂) as the distance D becomes shorter (D₂>D₁), as shown inFIG. 5. Here, the distance L is perpendicular to an optical axisextending from the reference point to the coupled plane, and thedistance D is a distance along the optical axis from the referencepoint. Therefore, a greater amount of adjustment can be obtained byperforming laser irradiation at a location closer to the reference pointalong the optical axis.

In a case where two or more of optical coupling components (such as thecondenser lens 30 and the incident face 41 in this embodiment) areemployed, the tolerance for the gap (x, y, θ), which is the opticalcoupling tolerance, varies among the optical coupling components. FIGS.6A and 6B show the optical coupling tolerances of the condenser lens 30and the incident face 41 of the ferrule 40 of this embodiment. FIG. 6Ais a graph showing the optical coupling tolerance of the condenser lens30. FIG. 6B is a graph showing the optical coupling tolerance of theincident face 41 of the ferrule 40. As can be seen from FIG. 6A, thetolerance curve of the condenser lens 30 is relatively tight. This meansthat the tolerance for the gaps (x, y, θ) is low. On the other hand, thetolerance curve of the incident face 41 of the ferrule 40 is relativelywide, as shown in FIG. 6B. Accordingly, the optical coupling toleranceof the incident face 41 of the ferrule 40 is greater than that of thecondenser lens 30.

For the above reason, the reference point is set on the side of the mainhousing 2, and the region on the surface of the trunk of the sub-housing50 that is closer to the reference point and is located between thecondenser lens 30 and the main housing 2, which is the region in whichthe optical axis C3 of the condenser lens 30 and the optical axis C4 ofthe ferrule 40 can be adjusted and a relatively large amount ofadjustment is made with a laser beam of a constant intensity, is set asa region for roughly performing optical axis adjustment (hereinafterreferred to as the “rough adjustment region”) in this embodiment, asshown in FIG. 7. Also, the region on the sub-housing 50 that is furtheraway from the reference point, which is the region in which the opticalaxis C4 of the ferrule can be adjusted and a relatively small amount ofadjustment is made with a laser beam of a constant intensity, is set asa region for finely performing optical axis adjustment (hereinafterreferred to as the “fine adjustment region”).

In this manner, multi-stage adjustment is made in the following regions:the rough adjustment region in which a relatively large amount ofadjustment is made with a laser beam of a constant intensity, and thefine adjustment region in which a relatively small amount of adjustmentis made with a laser beam of a constant intensity. Thus, with thisembodiment, optical axis adjustment can be readily performed with highefficiency and high precision.

However, the welded portions of the components of the sub-housing 50,especially the welded portion 54 between the first housing 51 and thesecond housing 52, should not be included in the rough adjustment regionand the fine adjustment region. This is because laser irradiation on thewelded portions adds to the distortion of the welded portions, and, as aresult, the bonding strength between components may decrease, or theoptical axes might return to the original tilting positions afteroptical axis adjustment. In a case where the surface of the trunk of thesub-housing 50 (excluding the welded portions) is deformed through laserirradiation, on the other hand, complicated stress strain is not causedinside, and therefore, the sub-housing 50 becomes resistant totemperature stress and changes with time. Thus, the occurrence of cracksand welding splits can be prevented. Accordingly, shifting of theoptical axes due to a temperature stress and changes with time can beprevented, and an optical module with higher long-term reliability andstability can be realized.

Also, in a case where the welded portions are to be irradiated with alaser beam (or where the welded portions are included in the roughadjustment region or the fine adjustment region), a laser beam (6A or6B) that exhibits great enough power to melt the welded points 5 a needsto be emitted. As a result, power control of the laser beam (6A or 6B)becomes difficult, and the possibility of laser irradiation with toomuch energy increases. If laser irradiation with too much energy isprovided, an optical axis deviation is caused on the opposite side fromthe deviation before the adjustment (or the optical axis tilts to theopposite side). To solve this problem, the laser emitting direction (thelaser emitting position) needs to be moved to the opposite side. In thatcase, a procedure of correcting the position of the optical outputdevice 1 or the laser irradiation unit needs to be added to the process,and the number of laser emitting times also increases. As a result, theprocess becomes complicated, and the production efficiency deteriorates.Further, in a case where optical axis adjustment is performed on thewelded portions, the amount of adjustment through laser irradiationcannot be controlled, due to inherent factors such as internal stressexisting in the welded portions. In this embodiment, on the other hand,the surface of the trunk of the sub-housing 50, excluding the weldedportions, is to be irradiated with a laser beam, so that the abovedescribed problems can be solved.

Referring now to FIGS. 8A and 8B, the relationship between the amount ofadjustment in the rough adjustment region and the amount of adjustmentin the fine adjustment region will be described. FIG. 8A is an innerperspective view of the sub-housing 50. FIG. 8B is a graph showing theamount of adjustment that can be made with a laser beam of a constantintensity with respect to the distance along the optical region from thereference point that is an optically coupled region on the opposite sideof the condenser lens 30 from the region between the incident face 41and the condenser lens 30. As shown in FIGS. 8A and 8B, the amount ofadjustment in the region between the main housing 2 and the condenserlens 30, which is the rough adjustment region, is greater than theamount of adjustment in the fine adjustment region, because the movementof the optical axis becomes greater as the deformation of thesub-housing 50 becomes greater due to the function of the condenser lens30. Also, in the rough adjustment region, the amount of adjustmentincreases as the distance from the reference point becomes shorter,which is true to the principles described above with reference to FIG.5. In the region between the condenser lens 30 and the incident face 41,which is the fine adjustment region, on the other hand, the amount ofadjustment is smaller than in the rough adjustment region, because thefunction of the condenser lens 30 does not affect the fine adjustmentregion. Also, in the fine adjustment region, the amount of adjustmentreduces as the distance from the reference point becomes longer. Takingadvantage of the optical characteristics and configurationcharacteristics described above, this embodiment can readily provide adesired amount of adjustment with high precision and high efficiency,through laser beam irradiation and control over the distance from thereference point.

In a case where a lens optical system that forms a magnification opticalsystem is employed in place of the condenser lens 30, however, theamount of movement of the optical axis caused by the deformation of thesub-housing 50 in the region on the reference point side of the lensoptical system (equivalent to the rough adjustment region) decreases dueto the function of the magnification optical system. The amount ofmovement of the optical axis caused by the deformation of thesub-housing 50 in the region on the opposite side of the lens opticalsystem from the reference point is not affected by the function of themagnification optical system. In view of this, the relationship shown inFIG. 8B might be reversed, n a case of a magnification optical system.Therefore, based on the positions of laser irradiation and thecharacteristics of a lens optical system, various modifications may bemade to the arrangement of the rough adjustment region and the fineadjustment region, with the lens optical system being provided inbetween. In this embodiment, such a lens optical system that opticallycouples two regions may be formed with a single lens or a combination oftwo or more lenses. The lens optical system may also be formed with anelectrooptical material that can function as a lens. In this embodiment,however, the lens optical system is a single optical coupling component,or a combination of two or more optical coupling components.

Also, in this embodiment, the thickness of the wall of the narrow part53 of the first housing 51 is smaller than any other part of thesub-housing 50, and the outer diameter of the cross section of thenarrow part 53 is smaller than any other part of the sub-housing 50.Therefore, the amount of adjustment obtained by irradiating the narrowpart 53 with a laser beam is greater than in the regions in theneighborhood of the narrow part 53, due to the effect of theconfiguration (see FIG. 8B).

Next, an optical axis adjusting method in accordance with thisembodiment will be described in detail. In the situation that will bedescribed below, laser welding is performed on the first housing 51 andthe second housing 52 that tilt with respect to each other. As mentionedearlier, the laser irradiation unit for laser-welding the first housing51 and the second housing 52 to each other may or may not be the same asthe laser irradiation unit for deforming the sub-housing 50. Further,the laser irradiation unit employed here may be a laser welding devicesuch as a YAG laser device.

FIG. 9 is an inner perspective view of a structure in which laserwelding has been performed on the first housing 51 and the secondhousing 52 tilting with respect to each other. As shown in FIG. 9,because of the laser welding performed on the first housing 51 and thesecond housing 52 tilting with respect to each other, a tilt is causedbetween the optical axis C2 and the optical axis C4. As a result, a gap(x, y, θ) including the horizontal element (x, y) and the angle element0 is caused between the optical axis C2 and the incident face 41(especially at the center of the incident face 41) of the ferrule 40.

In the first step of the optical axis adjusting method in accordancewith this embodiment, the rough adjustment region that is closer to areference point is irradiated with the laser beam 6A at least once, asshown in FIG. 10A. The reference point is the region that is located onthe opposite side of the condenser lens 30 from the region between theincident face 41 and the condenser lens 30. Through the laserirradiation, welded points 6 a are formed with a laser irradiationpattern shown in FIG. 10B. The laser irradiation with the laser beam 6Ais performed on the opposite side from the side toward which the opticalaxis C4 tilts with respect to the optical axis C2. Here, the laserirradiation is preferably started from the location closest to thereference point along the optical axis C2. By doing so, the shape of therough adjustment region of the sub-housing 50 is deformed, and the gap(x, y, θ) between the optical axis C2 and the center of the incidentface 41 is roughly corrected. At the same time, the focal point of thecondenser lens 30 approaches the optical axis C2, and the light quantityof the laser beam 3 to enter the ferrule 40 increases. The number oflaser irradiation times and the laser irradiation pattern in this stepare set so that the gap (x′, y′, θ′) after the adjustment is equal to orsmaller than the minimum value of the amount of adjustment to be made inthe rough adjustment region. As described above, the laser beam 6A isnot emitted onto the welded portion of each part of the sub-housing 50,especially onto the welded portion 54 between the first housing 51 andthe second housing 52.

Accordingly, a decrease in the joining strength of each part can beavoided, and the gap can be prevented from reappearing after the opticalaxis adjustment. Further, the laser beam 6A may or may not have the sameintensity as the laser beam 6B.

After the largest possible rough adjustment of an optical axis is madein the rough adjustment region, the operation moves on to the secondstep in this embodiment. In the second step, the fine adjustment regionis irradiated, at least once, with the laser beam 6B emitted from alaser irradiation unit, as shown in FIG. 11A, in which the laser modulebefore adjustment is shown by the broken lines. Welded points 6b arethen formed with a laser irradiation pattern shown in FIG. 11B. Thelaser irradiation with the laser beam 6B is performed on the oppositeside from the side toward which the optical axis C4 tilts with respectto the optical axis C2, as shown in FIG. 11A. Here, the laserirradiation is preferably started from the location closest to thereference point along the optical axis C2, as in the case shown in FIG.10A. By doing so, the shape of the fine adjustment region of thesub-housing 50 is deformed, and the gap (x′, y′, θ′) between the opticalaxis C2 and the center of the incident face 41 is corrected oreliminated. Accordingly, the positional relationship between the centerof the incident face 41 and the focal point of the condenser lens 30,which has been moved closer to the optical axis C2 in the first step, isfurther corrected so that the focal point of the condenser lens 30 issubstantially located in the center of the incident face 41. Thus, asufficient quantity of light can enter the ferrule 40. As in the firststep, the welded portion of each part of the sub-housing 50 is notirradiated with the laser beam 6B in this step. Accordingly, a decreasein the joining strength of each part can be avoided, and the gap can beprevented from reappearing after the optical axis adjustment. Further,the laser beam 6B may or may not have the same intensity as the laserbeam 6A and/or the laser beam 5A. In the above-mentioned manner, theoptical axes C2 and C4 are thus aligned. f

In a case where the locations of the rough adjustment region and thefine adjustment region are reversed, or, in a case where ademagnification optical system is employed as the lens optical system,the region (the rough adjustment region) between the lens optical systemand the incident face 41 is irradiated with a laser beam in the firststep, and the region (the fine adjustment region) located on theopposite side of the lens optical system from the rough adjustmentregion is irradiated with a laser beam in the second step.

Each of the above steps is carried out, while light outputted throughthe optical fiber 42 is being monitored at one end of the optical fiber42. FIG. 12 illustrates the structure of an apparatus (an optical axisadjusting apparatus 1A) that operates by the above optical axisadjusting method.

As shown in FIG. 12, the optical axis adjusting apparatus 1A includesthe optical output device 1, a light quantity detection device 91, acontrol computer 93, and a laser irradiation device 92. The lightquantity detection device 91 detects the light quantity of the laserbeam 3 transmitted through the optical fiber 42. The control computer 93controls the laser irradiation device 92, based on the light quantity ofthe laser beam 3 detected by the light quantity detection device 91.Under the control of the control computer 93, the laser irradiationdevice 92 irradiates the rough adjustment region with the laser beam 6A(the first step), and irradiates the fine adjustment region with thelaser beam 6B (the second step). With the optical axis adjustingapparatus 1A having such a structure, optical axis adjustment can beperformed, while deviations of the optical axes, the amount ofadjustment, and the quantity of light entering the ferrule 40, are beingmonitored.

The optical axis adjusting method of this embodiment can be included assome steps in the method of producing the optical output device 1.Accordingly, an optical module that has optical axes adjusted with highprecision and high efficiency can be readily produced, without anincrease in the number of production procedures.

As described so far, in accordance with this embodiment, an opticaloutput device that has optical axes adjusted stepwise with highprecision can be efficiently and easily obtained by carrying out thefirst step of irradiating a first region with a laser beam and thesecond step of irradiating a second region with a laser beam. With oneof two or more optical coupling components being a reference point (theincident face 41, for example), the region on the sub-housing 50 locatedcloser to the reference point is set as the first region (the roughadjustment region, for example), and the region on the sub-housing 50located further away from the reference point is set as the secondregion (the fine adjustment region, for example). Also, an optical axisadjusting apparatus that can efficiently and readily make adjustments tothe optical axes of an optical output device with high precision can berealized. Further, an optical axis adjusting method that can efficientlyand readily carry out high-precision optical axis adjustment on anoptical output device can be obtained. Still further, a method ofreadily and efficiently producing an optical output device that hasoptical axes adjusted with high precision can be realized.

This embodiment can be applied to an optical module that is interposedbetween optical fiber and a light-emitting element such as a laser chipor a light receiving chip, or between a laser chip and an opticalmodulator. This embodiment can also be applied to a passive opticalmodule such as an assembly of a lens and an optical isolator.

Second Embodiment

Next, a second embodiment of the present invention will be described indetail. The structure and operation of this embodiment are the same asthose of the first embodiment, unless specifically mentioned below.

In the first embodiment, largest possible adjustment is performed onoptical axes in the first step. However, optical axis adjustment made inthe rough adjustment region is relatively great in the adjustment stepwidth, or has a larger minimum adjustment value than in the fineadjustment region. If largest possible adjustment is performed, theadjusted optical axis C4 might tilt toward the opposite side from theoriginal titling position. In such a case, the emitting direction of thelaser beam 6B needs to be adjusted to the opposite side from theemitting direction of the laser beam 6A. As a result, the process ofmoving on to the second step might become complicated.

As already mentioned in the description of the first embodiment, theincident face 41 has a greater optical coupling tolerance than thecondenser lens 30. Accordingly, adjustment in the fine adjustment regionexhibits more stable characteristics with temperature stress and changeswith time than adjustment in the rough adjustment region.

In view of this, while the optical axis C4 is maintained in the samedirection as the original tilting direction (or the tilting directionprior to the first step), largest possible optical axis adjustment inthe situation is performed in the first step. For example, the totalamount of adjustment made in the second step should be greater than thetotal amount of adjustment made in the first step.

With this structure, there is no need to adjust the laser emittingdirection in the second step to the opposite direction from the laseremitting direction used in the first step, and the procedures can beprevented from becoming more complicated. Also, the above structure canexhibit stable characteristics with temperature stress and changes withtime. The other aspects and operations of this embodiment are the sameas those of the first embodiment, and explanation of them is omittedherein.

Third Embodiment

Next, a third embodiment of the present invention will be described indetail. This embodiment provides another example of an optical axisadjusting method. The structure and operation in accordance with thisembodiment are the same as those in accordance with the firstembodiment, unless specifically described below.

In the optical axis adjusting method in accordance with this embodiment,the same structure as the optical axis adjusting apparatus 1A of thefirst embodiment shown in FIG. 12 is employed. FIGS. 13A through 13Cillustrate the operation of the optical axis adjusting apparatus 1A ofthis embodiment. The following description mainly concerns the operationof the control computer 93.

In a first step of the optical axis adjusting method of this embodiment,the control computer 93 measures the light quantity of a laser beamoutputted from the optical output device 1 before optical axisadjustment is performed. The measurement is carried out with the lightquantity detection device 91, and the detected light quantity of thelaser beam will be hereinafter referred to as the detected lightquantity P1. In a second step, several spots on the sub-housing 50 areirradiated with a laser beam 6C emitted from the laser irradiationdevice 92, so that welded points 6 c are formed, as shown in FIG. 13A.The light quantity detection device 91 then measures the light quantityof a laser beam outputted from the optical output device 1. The lightquantity measured in this step will be hereinafter referred to as thedetected light quantity P2. At this point, the control computer 93stores parameters, such as the irradiation amount (the number ofirradiation times and the irradiation power) of the laser beam 6C at thetime of driving the laser irradiation device 92 and the irradiationperiod of time (each irradiation period or the total irradiation periodof the laser beam 6C). These parameters will be used to calculate theamount of optical axis adjustment (or the amount of recovery) in latersteps. The laser irradiation spots in the second step may be located inany of the following three regions: the rough adjustment region, thefine adjustment region, and the narrow part 53. In FIG. 13A, the laserirradiation spots are located in the narrow part 53, for example.

After the detected light quantity P1 and the detected light quantity P2are obtained, the operation of the control computer 93 moves on to athird step. In the third step, the control computer 93 calculates theamount of optical axis adjustment per unit energy, based on thedifference between the detected light quantity P1 and the detected lightquantity P2, and the total energy of the emitted laser beam 6C. In afourth step, based on the difference between a target light quantity(detected by the light quantity detection device 91) and the detectedlight quantity P2, the control computer 93 calculates the amount ofoptical axis adjustment that is necessary to achieve the target lightquantity.

In a fifth step, based on the calculated amount of optical axisadjustment, the control computer 93 determines the irradiation power,the number of irradiation times, and the irradiation spots of each oflaser beams 6D and 6E to form welded points 6d and 6e, respectively.

After that, in a sixth step (see FIG. 13B), the control computer 93controls the laser irradiation device 92 to perform rough adjustmentusing the irradiation power, the number of irradiation times, and theirradiation spots of the laser beam 6D that have been determined in thefifth step. In a seventh step (see FIG. 13C), the control computer 93controls the laser irradiation device 92 to perform fine adjustmentusing the irradiation power, the number of irradiation times, and theirradiation spots of the laser beam 6E that have been determined in thefifth step. In this manner, optical axis adjustment can be performed tomeet the necessary amount of optical axis adjustment to obtain a targetlight quantity. If there is no need to perform laser irradiation in thesixth or seventh step, or if the number of irradiation times is set atzero, it is possible to omit the step from the optical axis adjustingmethod.

As described so far, in this embodiment, the amount of optical axisadjustment necessary to obtain a target light quantity is calculated,and the control computer 93 automatically performs optical axisadjustment in accordance with the calculated amount of optical axisadjustment. The other aspects and operations of this embodiment are thesame as those of the first embodiment, and therefore, explanation ofthem is omitted herein.

Fourth Embodiment

Next, a fourth embodiment of the present invention will be described indetail. This embodiment provides another example of a method ofcalculating the necessary amount of optical axis adjustment to achieve atarget light quantity (equivalent to the first through fourth steps ofthe optical axis adjusting method in accordance with the thirdembodiment). The structure and operations of this embodiment are thesame as those of the foregoing embodiments, unless specificallydescribed below.

In the method of calculating the necessary amount of optical axisadjustment to achieve a target light quantity in accordance with thisembodiment, the control computer 93 measures the light quantity of alaser beam outputted from the optical output device 1 before opticalaxis adjustment is performed. The measurement is carried out with thelight quantity detection device 91, and the measured light quantity ofthe laser beam will be hereinafter referred to as the detected lightquantity P11. In a second step, the laser irradiation device 92 emitsthe laser beam 6D onto the rough adjustment region on the sub-housing50, and the light quantity detection device 91 then measures the lightquantity of a laser beam outputted from the optical output device 1. Thelight quantity measured in this step will be hereinafter referred to asthe detected light quantity P12. At this point, the control computer 93stores parameters, such as the irradiation amount (including the numberof irradiation times and the irradiation power) of the laser beam 6D atthe time of driving the laser irradiation device 92 and the irradiationperiod of time (each irradiation period or the total irradiation periodof the laser beam 6D). These parameters will be used to calculate theamount of optical axis adjustment (or the amount of recovery) in latersteps. In a third step, the laser irradiation device 92 emits the laserbeam 6E onto the fine adjustment region on the sub-housing 50, and thelight quantity detection device 91 then measures the light quantity of alaser beam outputted from the optical output device 1. The lightquantity measured in this step will be hereinafter referred to as thedetected light quantity P13. At this point, the control computer 93stores parameters, such as the irradiation amount (including the numberof irradiation times and the irradiation power) of the laser beam 6E atthe time of driving the laser irradiation device 92 and the irradiationperiod of time (each irradiation period or the total irradiation periodof the laser beam 6E). These parameters will be used to calculate theamount of optical axis adjustment in later steps.

After the detected light quantity P11, the detected light quantity P12,and the detected light quantity P13 are obtained, the operation of thecontrol computer 93 moves on to a fourth step. In the fourth step, thecontrol computer 93 calculates the amount of optical axis adjustment perunit energy at the time of laser irradiation in the rough adjustmentregion, based on the difference between the detected light quantity P11and the detected light quantity P12, and the total energy of the laserbeam 6D. In a fifth step, the control computer 93 calculates the amountof optical axis adjustment per unit energy at the time of laserirradiation in the fine adjustment region, based on the differencebetween the detected light quantity P12 and the detected light quantityP13, and the total energy of the laser beam 6E.

In a sixth step, the control computer 93 calculates the amount ofoptical axis adjustment necessary to achieve a target light quantity(detected by the light quantity detection device 91), based on thedifference between the target light quantity and the detected lightquantity P13. The operation after the sixth step in this optical axisadjusting method is the same as the operation after the fifth step inthe optical axis adjusting method of the third embodiment, andtherefore, explanation of it is omitted herein. Also, the other aspectsand operations of this embodiment are the same as those of the foregoingembodiments, and therefore, explanation them is omitted herein.

Fifth Embodiment

Next, a fifth embodiment of the present invention will be described indetail. In each of the foregoing embodiments, a lens optical system (thecondenser lens 30 in the first embodiment) for optically coupling tworegions is accommodated in the sub-housing 50 that is to be irradiatedwith a laser beam. In this embodiment, however, an optical couplingcomponent such as a lens optical system that optically couples tworegions is not provided in an object (a sub-housing 50B) to beirradiated with a laser beam. Instead, only the incident face 41 of theferrule 40 is provided as an optical coupling component.

FIG. 14A is an inner perspective view of the sub-housing 50B of thisembodiment. FIG. 14B is a graph showing the relationship between thedistance from the reference point on the sub-housing 50B and the amountof adjustment made with a laser beam of a constant intensity. As shownin FIG. 14A, the sub-housing 50B has a narrow part 53B near the bottom(on the side of the main housing 2). The outer diameter of the crosssection (a plane that is perpendicular to the light propagatingdirection) of the narrow part 53B is smaller than the outer diameter ofthe cross section (parallel to the cross section of the narrow part 53B)of any other part of the sub-housing 50B. Also, the thickness of theouter wall of the narrow part 53B is smaller than the thickness of theouter wall of any other part of the sub-housing 50B.

With the narrow part 53B, the amount of adjustment made with a laserbeam of a constant intensity can be increased in the corresponding part(see FIGS. 8A and 8B). In this embodiment, the region on the surface ofthe trunk of the sub-housing 50B that corresponds to the narrow part 53Bis set as the rough adjustment region, and the region that is closer tothe incident face 41 and is located on the surface of the trunk, notincluding the narrow part 53B, is set as the fine adjustment region.With this arrangement, multi-stage adjustment can be performed, as ineach of the foregoing embodiments, and optical axis adjustment can bereadily performed with high efficiency and high precision. The otheraspects of this embodiment are the same as those of the foregoingembodiments, and therefore, explanation of them is omitted herein.

Other Embodiments

In each of the foregoing embodiments, a cylindrical optical module(especially the sub-housing 50 and the sub-housing 50B) is employed.However, the present invention is not limited to cylindrical opticalmodules, but may be applied to optical modules having oval or polygonalcross sections. Further, the present invention may be applied to opticalmodules each having a flat substrate or a curved substrate as a holdingmember for optical coupling components.

In a case where a flat substrate is employed as the holding member, forexample, optical coupling components such as a lens optical system aremounted onto a surface (the outer surface) of the substrate. In thisstructure, the outer surface of the back surface of the substrate isirradiated with a laser beam emitted from a device such as a laserwelding device, so that the substrate as the holding member can bedeformed, as in each of the foregoing embodiments. Thus, a tilt angle ofan optical axis in two regions that are optically coupled can beadjusted. Although the substrate and the one or more optical couplingcomponents mounted onto the substrate can be regarded as one opticalmodule, a structure in which the substrate and the optical couplingcomponents are all housed in a housing body can be considered as oneoptical module.

Finally, some aspects of the present invention are summarized below.

The optical axis adjusting method for adjusting a tilt angle of anoptical axis in two regions that are optically coupled in a holdingmember, includes the steps of: roughly adjusting the optical axis byirradiating a first region on the holding member with a laser beam; andfinely adjusting the optical axis by irradiating a second region on theholding member with a laser beam, one of the two regions being areference point, the first region being located closer to the referencepoint, and the second region being located further from the referencepoint. The amounts of optical axis adjustment to be made through laserirradiation vary with the locations on the holding member along theoptical axis. Using the difference in the amount of adjustment, roughadjustment is performed in one of the first region and the secondregion, while fine adjustment is performed in the other one of the firstregion and the second region. By doing so, step-by-step optical axisadjustment can be performed, and efficient and highly precise opticalaxis adjustment can be readily realized.

The optical axis adjusting method for adjusting a tilt angle of anoptical axis in two regions that are optically coupled through a lensoptical system held by a holding member, comprising the steps of:irradiating a first region on the holding member with a laser beam, thefirst region being located on the same side of the lens optical systemas a reference point that is one of the two regions; and irradiating asecond region on the holding member with a laser beam, the second regionbeing located on the opposite side of the lens optical system from thereference point, one of the first region and the second region being aregion in which the tilt angle of the optical axis is roughly adjusted,and the other one of the first region and the second region being aregion in which the tilt angle of the optical axis is finely adjusted.The amounts of optical axis adjustment to be made through laserirradiation vary with the locations on the holding member along theoptical axis. Especially between two regions partitioned by a lensoptical system, the difference in the amount of adjustment to be made isvery large. Using the difference in the amount of adjustment, roughadjustment is performed in one of the first region and the secondregion, while fine adjustment is performed in the other one of the firstregion and the second region. By doing so, step-by-step optical axisadjustment can be performed, and efficient and highly precise opticalaxis adjustment can be readily realized.

The optical axis adjusting method may be configured so that amagnification optical system is employed as the lens optical system,and/or the lens optical system has a focal length that is longer on theside of the reference point and shorter on the side of a coupled plane,so that the first region is set as a region in which the fine adjustmentis performed, and that the second region is set as a region in which therough adjustment is performed. In the case where the lens optical systemis a magnification optical system, the degree of optical axis couplingper unit area on the coupled plane is smaller (if the reference point isthe light source, the light quantity per unit area becomes smaller) thanin a case where the lens optical system is not employed. Accordingly, ifthe light quantity obtained as a result of moving an optical axisthrough laser irradiation in the first region is smaller than the lightquantity obtained as a result of moving an optical axis through laserirradiation in the second region, the first region serves as the fineadjustment region while the second region serves as the rough adjustmentregion. Also, in the case where the focal length of the lens opticalsystem is longer on the side of the coupled plane than on the side ofthe reference point, the amount of optical axis movement on the coupledplane is smaller than in a case where the lens optical system is notemployed. Accordingly, when the amount of optical axis movement issmaller than the amount of optical axis movement obtained through laserirradiation in the first region, the first region serves as the fineadjustment region while the second region serves as the rough adjustmentregion. As the lens optical system is set in the above manner, a higherdegree of freedom can be allowed for optical axis adjustment inaccordance with the present invention.

The optical axis adjusting method as claimed in claim 2, wherein theamount of adjustment of light quantity on a coupled plane to becontrolled by irradiating the first region with a laser beam isdetermined by whether the lens optical system is a magnification opticalsystem or a demagnification optical system and/or the ratio of the focallength of the lens optical system on the side of the reference point tothe focal length of the lens optical system on the side of the coupledplane. In the case where the lens optical system is a demagnificationoptical system, the degree of optical axis coupling per unit area on thecoupled plane is greater (if the reference point is the light source,the light quantity per unit area is greater) than in a case where thelens optical system is not employed. Accordingly, when the optical axisis moved through laser irradiation in the first region, the lightquantity that varies on the coupled plane becomes greater. Also, in acase where the focal length of the lens optical system is short on theside of the reference point and long on the side of the coupled plane,the amount of movement of an optical axis through laser irradiation inthe first region is greater than in a case where the lens optical systemis not employed. In a case where the focal length of the lens opticalsystem is long on the side of the reference point and short on the sideof the coupled plane, the amount of movement of the optical axis issmaller than in a case where the lens optical system is not employed. Asthe focal length ratio is set by selecting the type of the lens opticalsystem in the above manner, the amount of optical axis adjustment to bemade can be arbitrarily set.

The optical axis adjusting method may be configured so that the step ofroughly adjusting a tilt angle of the optical axis is carried out priorto the step of finely adjusting the tilt angle of the optical axis. Thefine adjustment is performed after the rough adjustment, so that opticalaxis adjustment can be performed with higher efficiency and higherprecision.

The optical axis adjusting method may be configured so that one or bothof the above-mentioned steps are carried out by emitting a laser beammore than once along the surrounding area of the first region or thesecond region that surrounds the optical axis.

The optical axis adjusting method may be configured so that one or bothof the steps are carried out by emitting a laser beam more than onceonto different spots in the longitudinal direction of the optical axisin the first region or the second region. A laser beam is emitted morethan once onto different spots along the optical axis in the firstregion or the second region, so that finer adjustment can be performed,and that higher precision can be achieved in the optical axisadjustment.

The optical axis adjusting method may be configured so that: the holdingmember is an assembly that is produced by welding two or more members;and both of the steps are carried out by emitting the laser beam ontoregions excluding the welded portion of the holding member. If a laserbeam is repeatedly emitted onto the welded portion, deformation occursin various spots of the welded portion. As a result, the joiningstrength between the members might decrease, or the adjusted opticalaxis might return to the previous position. In the case where theholding member, excluding the welded portion, is deformed through laserirradiation, stress strain does not occur inside. Accordingly, adverseinfluence of temperature stress and a lapse of time can be reduced, andcracks or weld cracks can be prevented. Thus, optical axis movement dueto temperature stress and a lapse of time can be restrained, and higherlong-term reliability and stability can be achieved.

The optical axis adjusting method may be configured so that: the holdingmember is an assembly that is produced by welding two or more members;and both of the steps are carried out with a laser irradiation unit thatis also used for welding the holding member. Using the same laserirradiation unit for assembling the holding member and adjusting anoptical axis, the step of assembling the holding member and the steps ofadjusting the optical axis can be carried out in a series of procedures.Thus, the entire process can be simplified.

The optical axis adjusting method may be configured so that: the holdingmember is an assembly that is produced by welding two or more members;and both of the steps are carried out with a laser irradiation unit thatis different from a laser irradiation unit used for welding the holdingmember.

The optical axis adjusting method may be configured so that theintensity of the laser beam used in the step of roughly adjusting theoptical axis is the same as or different from the intensity of the laserbeam used in the step of finely adjusting the optical axis.

The optical axis adjusting method may be configured so as to furtherinclude the steps of: detecting an amount of adjustment to be made tothe optical axis by irradiating the holding member with a laser beam,prior to the step of roughly adjusting the optical axis and the step offinely adjusting the optical axis; and based on the detected amount ofadjustment, setting at least one of an irradiation quantity of the laserbeam, an irradiation time, and an irradiation position that are to beemployed in the step of roughly adjusting the optical axis and/or thestep of finely adjusting the optical axis. The amount of adjustment tobe made to the optical axis through laser irradiation is detected priorto actual optical axis adjustment. In this manner, the laser beam can bereadily controlled in the later steps, using the detected amount as thereference amount. Thus, optical axis adjustment can be performed withhigh efficiency and high precision.

The optical axis adjusting method may be configured so that the amountof adjustment is detected by emitting the laser beam onto a regionbetween the first region and the second region.

The optical axis adjusting method may be configured so as to furthercomprise the steps of: detecting a first amount of adjustment to be madeto the optical axis by irradiating the first region with a laser beam,prior to the step of roughly adjusting the optical axis and the step offinely adjusting the optical axis; detecting a second amount ofadjustment to be made to the optical axis by irradiating the secondregion with a laser beam, prior to the step of roughly adjusting theoptical axis and the step of finely adjusting the optical axis; based onthe first amount of adjustment, setting at least one of an irradiationquantity of the laser beam, an irradiation time, and an irradiationposition that are to be employed in the step of roughly adjusting theoptical axis; and based on the second amount of adjustment, setting atleast one of an irradiation quantity of the laser beam, an irradiationtime, and an irradiation position that are to be employed in the step offinely adjusting the optical axis. The amount of adjustment to be madeto the optical axis through laser irradiation is detected prior toactual optical axis adjustment. In this manner, the laser beam can bereadily controlled in the later steps, using the detected amount as thereference amount. Thus, optical axis adjustment can be performed withhigh efficiency and high precision.

The optical axis adjusting method may be configured so as to furtherinclude the steps of: detecting the amount of adjustment made to theoptical axis in the step of roughly adjusting the optical axis; andbased on the detected amount of adjustment, setting at least one of anirradiation quantity of the laser beam, an irradiation time, and anirradiation position that are to be employed in the step of roughlyadjusting the optical axis or the step of finely adjusting the opticalaxis. The amount of adjustment made to the optical axis in the step ofroughly adjusting the optical axis is detected, so that the laser beamcan be readily controlled in the later steps, using the detected amountas the reference amount. Thus, optical axis adjustment can be performedwith higher efficiency and higher precision.

The method of producing an optical module of the present inventionincludes the step of adjusting a tilt angle of an optical axis in tworegions that are optically coupled, the step of adjusting a tilt anglebeing carried out by an optical axis adjusting method that includes thesteps of: roughly adjusting the optical axis by irradiating a firstregion on the holding member with a laser beam; and finely adjusting theoptical axis by irradiating a second region on the holding member with alaser beam, one of the two regions being a reference point, the firstregion being located closer to the reference point, and the secondregion being located further from the reference point. In this manner,the above described optical axis adjusting method is incorporated intothe method of producing an optical module. Thus, optical modules thathave optical axes adjusted with high precision can be readily andefficiently produced.

As described above, the present invention can be applied to variousoptical modules, regardless of the shapes and configurations of theholding members. These optical modules can perform optical axisadjustment just as well as the optical modules of the foregoingembodiments.

Although a few preferred embodiments of the present invention have beenshown and described, it would be appreciated by those skilled in the artthat changes may be made in these embodiments without departing from theprinciples and spirit of the invention, the scope of which is defined inthe claims and their equivalents.

1. An optical axis adjusting method for adjusting a tilt angle of anoptical axis in two regions that are optically coupled in a holdingmember, comprising the steps of: roughly adjusting the optical axis byirradiating a first region on the holding member with a laser beam; andfinely adjusting the optical axis by irradiating a second region on theholding member with a laser beam, one of the two regions being areference point, the first region being located closer to the referencepoint, and the second region being located further from the referencepoint.
 2. An optical axis adjusting method for adjusting a tilt angle ofan optical axis in two regions that are optically coupled through a lensoptical system held by a holding member, comprising the steps of:irradiating a first region on the holding member with a laser beam, thefirst region being located on the same side of the lens optical systemas a reference point that is one of the two regions; and irradiating asecond region on the holding member with a laser beam, the second regionbeing located on the opposite side of the lens optical system from thereference point, one of the first region and the second region being aregion in which the tilt angle of the optical axis is roughly adjusted,and the other one of the first region and the second region being aregion in which the tilt angle of the optical axis is finely adjusted.3. The optical axis adjusting method as claimed in claim 2, wherein amagnification optical system is employed as the lens optical system,and/or the lens optical system has a focal length that is longer on theside of the reference point and shorter on the side of a coupled plane,so that the first region is set as a region in which the fine adjustmentis performed, and that the second region is set as a region in which therough adjustment is performed.
 4. The optical axis adjusting method asclaimed in claim 2, wherein the amount of adjustment of light quantityon a coupled plane to be controlled by irradiating the first region witha laser beam is determined by whether the lens optical system is amagnification optical system or a demagnification optical system and/orthe ratio of the focal length of the lens optical system on the side ofthe reference point to the focal length of the lens optical system onthe side of the coupled plane.
 5. The optical axis adjusting method asclaimed in claim 1, wherein the step of roughly adjusting a tilt angleof the optical axis is carried out prior to the step of finely adjustingthe tilt angle of the optical axis.
 6. The optical axis adjusting methodas claimed in claim 1, wherein one or both of the steps are carried outby emitting a laser beam more than once along the surrounding area ofthe first region or the second region that surrounds the optical axis.7. The optical axis adjusting method as claimed in claim 1, wherein oneor both of the steps are carried out by emitting a laser beam more thanonce onto different spots in the longitudinal direction of the opticalaxis in the first region or the second region.
 8. The optical axisadjusting method as claimed in claim 1 or claim 2, wherein: the holdingmember is an assembly that is produced by welding two or more members;and both of the steps are carried out by emitting the laser beam ontoregions excluding the welded portion of the holding member.
 9. Theoptical axis adjusting method as claimed in claim 1 or claim 2, wherein:the holding member is an assembly that is produced by welding two ormore members; and both of the steps are carried out with a laserirradiation unit that is also used for welding the holding member. 10.The optical axis adjusting method as claimed in claim 1 or claim 2,wherein: the holding member is an assembly that is produced by weldingtwo or more members; and both of the steps are carried out with a laserirradiation unit that is different from a laser irradiation unit usedfor welding the holding member.
 11. The optical axis adjusting method asclaimed in claim 1 or claim 2, wherein the intensity of the laser beamused in the step of roughly adjusting the optical axis is the same as ordifferent from the intensity of the laser beam used in the step offinely adjusting the optical axis.
 12. The optical axis adjusting methodas claimed in claim 1 or claim 2, further comprising the steps of:detecting an amount of adjustment to be made to the optical axis byirradiating the holding member with a laser beam, prior to the step ofroughly adjusting the optical axis and the step of finely adjusting theoptical axis; and based on the detected amount of adjustment, setting atleast one of an irradiation quantity of the laser beam, an irradiationtime, and an irradiation position that are to be employed in the step ofroughly adjusting the optical axis and/or the step of finely adjustingthe optical axis.
 13. The optical axis adjusting method as claimed inclaim 12, wherein the amount of adjustment is detected by emitting thelaser beam onto a region between the first region and the second region.14. The optical axis adjusting method as claimed in claim 1 or claim 2,further comprising the steps of: detecting a first amount of adjustmentto be made to the optical axis by irradiating the first region with alaser beam, prior to the step of roughly adjusting the optical axis andthe step of finely adjusting the optical axis; detecting a second amountof adjustment to be made to the optical axis by irradiating the secondregion with a laser beam, prior to the step of roughly adjusting theoptical axis and the step of finely adjusting the optical axis; based onthe first amount of adjustment, setting at least one of an irradiationquantity of the laser beam, an irradiation time, and an irradiationposition that are to be employed in the step of roughly adjusting theoptical axis; and based on the second amount of adjustment, setting atleast one of an irradiation quantity of the laser beam, an irradiationtime, and an irradiation position that are to be employed in the step offinely adjusting the optical axis.
 15. The optical axis adjusting methodas claimed in claim 2, further comprising the steps of: detecting theamount of adjustment made to the optical axis in the step of roughlyadjusting the optical axis; and based on the detected amount ofadjustment, setting at least one of an irradiation quantity of the laserbeam, an irradiation time, and an irradiation position that are to beemployed in the step of roughly adjusting the optical axis or the stepof finely adjusting the optical axis.
 16. A method of producing anoptical module comprising the step of adjusting a tilt angle of anoptical axis in two regions that are optically coupled, the step ofadjusting includes the steps of: roughly adjusting the optical axis byirradiating a first region on the holding member with a laser beam; andfinely adjusting the optical axis by irradiating a second region on theholding member with a laser beam, one of the two regions being areference point, the first region being located closer to the referencepoint, and the second region being located further from the referencepoint.
 17. An optical axis adjusting apparatus that adjusts a tilt angleof an optical axis in two regions that are optically coupled in aholding member, the optical axis adjusting apparatus comprising a laserirradiation unit that outputs a laser beam, with one of the two regionsbeing a reference point, one of a first region and a second region onthe holding member being a region in which rough adjustment isperformed, the other one of the first region and the second region beinga region in which fine adjustment is performed, the second region beinglocated further from the reference point along the optical axis.
 18. Theoptical axis adjusting apparatus as claimed in claim 17, wherein: theholding member is an assembly that is produced by welding two or moremembers; and the laser irradiation unit outputs a laser beam that isused for welding the two or more members to form the holding member. 19.The optical axis adjusting apparatus as claimed in claim 17, wherein:the holding member is an assembly that is produced by welding two ormore members; and the two or more members are welded with a laser beamemitted from a laser irradiation unit that is different from the laserirradiation unit that irradiates the first region or the second regionwith the laser beam.
 20. The optical axis adjusting apparatus as claimedin claim 17, wherein a lens optical system is interposed between the tworegions optically coupled in the holding member.
 21. An optical modulecomprising a holding member that holds an optical axis of at least oneof two regions that are optically coupled, one of the two regions beinga reference point, one of a first region and a second region on theholding member being a rough adjustment region in which a tilt angle ofthe optical axis is roughly adjusted through laser irradiation, theother one of the first region and the second region being a fineadjustment region in which the tilt angle of the optical axis is finelyadjusted through laser irradiation, the second region being locatedfurther from the reference point along the optical axis.
 22. The opticalmodule as claimed in claim 21, wherein the thickness of the holdingmember is smaller in one of the first region and the second region thanin regions other than the one of the first region and the second region,or the outer diameter of the holding member is smaller in at least oneof the first region and the second region than in regions other than theone of the first region and the second region.
 23. The optical module asclaimed in claim 21, wherein: the holding member is an assembly that isproduced by welding two or more members; and the first region and thesecond region exclude the welded portion of the holding member.
 24. Theoptical module as claimed in claim 21, wherein a lens optical system isinterposed between the first region and the second region.
 25. A methodof producing an optical module comprising the step of adjusting a tiltangle of an optical axis in two regions that are optically coupledthrough a lens optical system held by a holding member, the step ofadjusting comprising the steps of: irradiating a first region on theholding member with a laser beam, the first region being located on thesame side of the lens optical system as a reference point that is one ofthe two regions; and irradiating a second region on the holding memberwith a laser beam, the second region being located on the opposite sideof the lens optical system from the reference point, one of the firstregion and the second region being a region in which the tilt angle ofthe optical axis is roughly adjusted, and the other one of the firstregion and the second region being a region in which the tilt angle ofthe optical axis is finely adjusted.